System and method for recovering precious metals from precursor-type ore materials

ABSTRACT

The present invention provides a system and method for recovering a precious metal from a geologic material. The system and method may include combining a geologic material containing a precious metal present in a non-bulk state with a first stage flux composition. The combination may be milled to provide a first stage mixture. The first stage mixture may be sintered for a first period of time at a first temperature and a second period of time at a second temperature. The second temperature may be greater than the first temperature. Sintering may promote the transition of a portion of the precious metal from a non-bulk state to a bulk state. A first stage sintered material may be recovered with a content of at least about 0.15 weight percent of the precious metal in the bulk state.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of prior U.S. applicationSer. No. 14/261,286, filed Apr. 24, 2014, which claims the benefit ofU.S. Provisional Application No. 61/949,174, filed Mar. 6, 2014, each ofwhich is incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not applicable.

BACKGROUND OF THE INVENTION

The disclosure relates, in general, to the recovery of a target materialfrom a geologic composition and, more particularly, to a system andmethod for the recovery of precious metals from a precursor type ore.

Gold (Au) is one of the most highly sought after elements mined from theearth and is used as currency, in commercial settings (e.g., jewelry,arts and crafts), and in industrial settings (e.g., electronics,medicine, optics). At standard conditions, gold exists as a solid,generally non-reactive chemical element. Gold can be found in nature asnuggets or grains, in rocks, in veins, in alluvial deposits, and inminerals as gold compounds.

Existing techniques for mining of gold ore can be economical withmaterial containing as little as 0.5 ppm gold even though at thisconcentration, the gold may be invisible to the naked eye. Variousconcentrating techniques include leaching such as with an aqueoussolution of cyanide to form a water soluble coordination complexaccording to the following reaction:

4Au+8NaCN+O₂+2H₂O→4Na[Au(CN)₂]+4NaOH.

The gold can then be separated from the cyanide solution and the cyanideremediated to ammonia. More refractory gold containing ore may besubjected to various pretreatments including the application of heat,microbes, pressure, or mechanical grinding.

More recently, it has been discovered that various geologic materialsmay contain gold in a state that is undetectable using traditionalanalytical techniques such as inductively coupled plasma, atomicabsorption spectroscopy, and fire assays/cupellation, the last of whichis an accepted standard for valuing gold ore.

As described by van Deventer (Minerals Engineering 2013, vol. 53, pp.266-275), a number of studies exist where fire assays were conducted ongeologic materials such as mine tailings (i.e., gangue—the leftover orematerial after separation from the valuable fraction of the ore), coalcombustion products or CCPs (e.g., fly ash, flue-gas desulfurizationmaterials, bottom ash, boiler slag) and other precursor-type orematerials. Generally, fire assaying such materials indicates that thesamples contain an infinitesimal or undetectable amount of gold. In onestudy, Seredin et al. reported gold concentrations on the order of about100 parts per billion (0.00001 wt %) in fly ash (Mineralium Deposita2014, vol. 49, pp. 1-6). In another study, a fire assay was only able toidentify about 0.01 ppm gold. However, after various treatment steps, itwas possible to recover nearly 70 ppm gold from the sample. Theseresults show that fire assay is an inaccurate and ineffective techniquefor determining the gold content of such geologic materials.

One possible explanation for the ineffectiveness of the aforementionedanalysis techniques is that the gold may exist in a non-bulk physicalstate. It is well known that bulk materials tend to have a particularset of physical and chemical properties. In one aspect, the propertiesof bulk change as the scale decreases and the fraction of atoms at thesurface of a material becomes significant. Thus, when atomic andnanoscale particles are isolated from the bulk material, the physicaland chemical behavior of these particles can deviate. For example, goldnanoparticles are capable of forming colloidal suspensions assolvent-surface interactions overcome differences in density. Moreover,colloidal suspensions of submicron-sized gold particles can range inappearance from red to blue to purple depending on the particle size.Therefore, if the gold particles are present in the geologic material ina non-bulk physical state, it may not be possible to perform an accuratedetermination of the gold content of a sample using standard analyticaltechniques.

Given the commercial and industrial value of gold and the potential thatthere may be significant quantities of the element present in geologicmaterials including mine tailings and CCPs, it may be beneficial torecover the gold and other precious metals from these geologicmaterials. However, given that the precious metals may be present in anon-bulk physical state which is not amenable to traditional analyticaltechniques, there is a need for a system and a method to transform theprecious metals into a bulk physical state so that they may beaccurately detected and recovered in an economical fashion.

SUMMARY OF THE INVENTION

The present invention overcomes the aforementioned drawbacks byproviding a system and method for the detection and recovery of gold ina non-bulk physical state. In accordance with one aspect of the presentdisclosure, a method is provided for recovering a precious metal from ageologic material. The method includes the steps of combining a geologicmaterial including at least one precious metal in a non-bulk state witha first stage flux composition to form a first combination. The methodfurther includes milling the first combination to provide a first stagemixture, and sintering the first stage mixture according to a firstsintering profile. The first sintering profile causes a portion of theprecious metal to agglomerate within the first stage mixture into a bulkstate of the precious metal, the at least one precious metal having inthe bulk state a greater weight percent of the first stage mixture thanthe at least one precious metal had prior to sintering the first stagemixture.

In one aspect, a first stage sintered material includes at least about0.15 weight percent of the at least one precious metal in the bulkstate. In another aspect, the at least one precious metal is selectedfrom gold, silver and platinum group metals. A portion of the at leastone precious metal is present as atomic clusters bonded to amorphouscolloidal silica. In still another aspect, the first stage fluxcomposition and the one or more sintering profiles are selected toseparate the atomic clusters from the amorphous colloidal silica. In yetanother aspect, the geologic material is selected from mine tailings andcoal combustion products.

In one aspect, the first stage flux composition includes at least one ofsodium tetraborate, calcium fluoride, lead oxide, and activated carbon.In another aspect, the first combination comprises about 25 to about 75weight percent of the geologic material, about 25 to about 75 weightpercent of the first stage flux composition and about 0 to about 10weight percent of a seed material. In yet another aspect, the seedmaterial includes one of gold powder and gold ore. In still anotheraspect, the first sintering profile includes a first period of time at afirst temperature and a second period of time at a second temperature.The second temperature is greater than the first temperature. In afurther aspect, the first temperature is at least about 500 degreesCelsius, and wherein the second temperature is at least about 600degrees Celsius.

In some embodiments, the method includes combining into a secondcombination the first stage sintered material and a second stage fluxcomposition. The method further includes milling the second combinationto provide a second stage mixture, and sintering the second stagemixture according to a second sintering profile. The second sinteringprofile causes a portion of the at least one precious metal toagglomerate within the second stage mixture, the at least one preciousmetal having a greater weight percent of the second stage mixture thanthe at least one precious metal had prior to sintering the second stagemixture. The method may include recovering a second stage sinteredmaterial including at least about 1 weight percent of the at least oneprecious metal.

In one aspect, the second stage flux composition includes at least oneof sodium tetraborate, calcium fluoride, lead oxide, and activatedcarbon. In another aspect, the second combination comprises about 65 toabout 95 weight percent of the first stage sintered material, about 5 toabout 35 weight percent of the second stage flux composition and about 0to about 10 weight percent of a seed material. In yet another aspect,the seed material includes one of gold powder and gold ore.

In accordance with another aspect of the present disclosure, a method isprovided for recovering a precious metal from a geologic material. Themethod includes combining into a first combination about 25 to about 75weight percent of a geologic material including gold present in anon-bulk state, about 25 to about 75 weight percent of a first stageflux composition, and about 0 to about 10 weight percent of gold ore.The method further includes milling the first combination to provide afirst stage mixture, and sintering the first stage mixture for a firstperiod of time at a first temperature, a second period of time at asecond temperature, and a third period of time at a third temperature.The second temperature is greater than the first temperature, and thethird temperature is greater than the second temperature. The methodfurther includes recovering a first stage sintered material including atleast about 0.15 weight percent of gold metal transitioned duringsintering from a non-bulk state to a bulk state.

In one aspect, the geologic material is selected from mine tailings andcoal combustion products. In another aspect, the first stage fluxcomposition includes calcium fluoride and at least one of sodiumtetraborate, lead oxide, and activated carbon.

In yet another aspect, the method includes combining about 65 to about95 weight percent of the first stage sintered material, about 5 to about35 weight percent of a second stage flux composition, and about 0 toabout 10 weight percent of gold ore. The method further includes millingthe combination including the first stage sintered material to provide asecond stage mixture, sintering the second stage mixture as in the caseof the first stage mixture, and recovering a second stage sinteredmaterial including at least about 1 weight percent of gold metaltransitioned during the sintering steps from the non-bulk state to thebulk state. In one aspect, the second stage flux composition includescalcium fluoride and at least one of sodium tetraborate, lead oxide, andactivated carbon.

In accordance with another aspect of the present disclosure, a method isprovided for recovering a precious metal from a geologic material. Themethod includes forming a slurry including a geologic material includingat least one precious metal, the at least one precious metal beingpresent in a non-bulk state, and a surfactant. The method furtherincludes agitating the slurry, recovering a solid fraction from theagitated slurry, and sintering the solid fraction according to a firstsintering profile that causes a portion of the at least one preciousmetal to agglomerate within the solid fraction into a bulk state of theat least one precious metal, the at least one precious metal having inthe bulk state a greater weight percent of the solid fraction than theat least one precious metal had prior to sintering the solid fraction.

The slurry may include urea. The urea is added to the slurry to providea final concentration of about 1 gram per liter to 100 grams per liter.The precious metal may be selected from gold, silver and platinum groupmetals. A portion of the precious metal may be present as atomicclusters bonded to amorphous colloidal silica, and the composition ofthe slurry and the first sintering profile may be selected to separatethe atomic clusters from the amorphous colloidal silica. The geologicmaterial may be selected from mine tailings and coal combustionproducts. The surfactant may be added to the slurry to a finalconcentration of about 0.01% to about 1% on a volume per volume basis.The slurry may comprise about 50 g of the geologic material per 1 literof water. The first sintering profile may include a first period of timeat a first temperature and a second period of time at a secondtemperature, wherein the second temperature is greater than the firsttemperature. The first temperature may be at least about 260 degreesCelsius, and the second temperature may be at least about 680 degreesCelsius. The method may further include washing the geologic materialprior to forming the slurry. The surfactant may be polyethylene glycolp-(1,1,3,3-tetramethylbutyl)-phenyl ether.

In accordance with another aspect of the present disclosure, a method isprovided for recovering gold from a geologic material. The methodincludes combining, into a first slurry, a geologic material includinggold present in a non-bulk state, and about 1 liter of water per 50grams of the geologic material. The method further includes agitatingthe first slurry, recovering a first solid fraction from the firstslurry, and combining, into a second slurry, the first solid fraction,about 1 liter of water per 50 g of the geologic material, about 1 gramper liter to about 100 grams per liter of urea, and about 0.01% to about1% of a non-ionic surfactant on a volume per volume basis. The methodfurther includes agitating the second slurry, recovering a second solidfraction from the second slurry, sintering the second solid fraction fora first period of time at a first temperature, a second period of timeat a second temperature, and a third period of time at a thirdtemperature, wherein the second temperature is greater than the firsttemperature, and the third temperature is greater than the secondtemperature and recovering a sintered material including at least about0.15 weight percent of gold metal in a bulk state.

The geologic material may be selected from mine tailings and coalcombustion products. The second slurry may comprise about 10 grams perliter of urea. The second slurry may comprise about 0.1% of thesurfactant on a volume per volume basis. The first temperature may be atleast about 260 degrees Celsius, and the second temperature may be atleast about 680 degrees Celsius, and the third temperature may be atleast about 1090 degrees Celsius. The surfactant may be polyethyleneglycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether. The method may furtherinclude a step of mechanically attriting the sintered material.

The foregoing and other aspects and advantages of the invention willappear from the following description. In the description, reference ismade to the accompanying drawings which form a part hereof, and in whichthere is shown by way of illustration a preferred embodiment of theinvention. Such embodiment does not necessarily represent the full scopeof the invention, however, and reference is made therefore to the claimsand herein for interpreting the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is schematic flow chart illustrating an example method forrecovering precious metals from precursor-type ore materials.

FIG. 2 is a schematic flow chart illustrating another example method forrecovering precious metals from precursor-type ore materials.

FIG. 3 is a schematic flow chart illustrating yet another example methodfor recovering precious metals from precursor-type ore materials.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is presented in several varying embodiments in thefollowing description with reference to the Figures, in which likenumbers represent the same or similar elements. Reference throughoutthis specification to “one embodiment,” “an embodiment,” or similarlanguage means that a particular feature, structure, or characteristicdescribed in connection with the embodiment is included in at least oneembodiment of the present invention. Thus, appearances of the phrases“in one embodiment,” “in an embodiment,” and similar language throughoutthis specification may, but do not necessarily, all refer to the sameembodiment.

The described features, structures, or characteristics of the inventionmay be combined in any suitable manner in one or more embodiments. Inthe following description, numerous specific details are recited toprovide a thorough understanding of embodiments of the system. Oneskilled in the relevant art will recognize, however, that the system andmethod may both be practiced without one or more of the specificdetails, or with other methods, components, materials, and so forth. Inother instances, well-known structures, materials, or operations are notshown or described in detail to avoid obscuring aspects of theinvention.

In general, one aspect of the present disclosure includes a system andmethod for recovering a target material from a composition containingthe target material. Accordingly, in some embodiments, precious metalssuch as gold, silver and platinum group metals may be recovered from aprecursor-type ore (PTO). A PTO may be understood as a geologic materialcontaining a substantial amount of naturally formed precious metalelements existing in a non-bulk state. A non-bulk state may beunderstood as a particle existing in a physical or chemical state wherethe behavior of the particle is characteristically different from thatof the behavior of the bulk material (i.e., the bulk state). In oneaspect, the particle size or composition may influence whether theparticle is in a non-bulk state. For example, whereas bulk quantities ofgold have a characteristic yellow color, a solution of monodispersecolloidal gold particles with a particle size of about 100 nm willexhibit a red color with a peak emission wavelength of about 572 nm. Anon-bulk state may also include single element atomic clusters bonded toamorphous colloidal silica present in a PTO. Examples of PTO materialscan include CCPs, mine tailings, and the like.

In the present disclosure, one or more steps, methods or techniques mayrefer to a specific example process such as the recovery of gold fromfly ash. While one particular element or PTO may be referred to, thepresent disclosure is applicable to the recovery a number of preciousmetals from a variety of materials where these metals may be present ina non-bulk state. Therefore, the examples described herein are includedby way of illustration and are not meant to limit the scope of thepresent disclosure.

One aspect of a method according to the present disclosure may includeproviding a PTO material. The PTO may be a geologic material includingat least one precious metal present in a non-bulk state. In someembodiments, the PTO may be prepared with a given average particle sizeor distribution. Accordingly, a given particle size may be preparedthrough the use of a standard mesh or sieve series.

Sieve sizes are generally regulated by standards, such as internationalstandards ISO 565:1990 and ISO 3310-1:2000, European standard EN 933-1,and U.S. standard ASTM E11:01. In the United States, particle sizes maybe classified using the U.S. Sieve Series as well as the Tyler StandardSieve Series. With respect to U.S. standard mesh sizes, increasing meshnumber generally correspond with decreasing particles sizes. Forexample, a U.S. No. 200 mesh is equivalent to a 200 Tyler mesh isequivalent to a 0.074 mm (0.0029 inches) opening, whereas a U.S. No. 325mesh is equivalent to a 325 Tyler mesh is equivalent to a 0.044 mm(0.0017 inches) opening.

In some embodiments, the PTO may be prepared with a particle sizeaccording to a minimum U.S. mesh size of about 200 to about 300.Consequently, the maximum particle size of the PTO material may be about50 μm to about 75 μm. Other PTO particle sizes may also be used. Forexample, a given starting particle size may be chosen based on a methodselected for combining or milling the PTO with another material in asubsequent process.

In some embodiments of the present disclosure, the PTO material may becombined with a flux composition. A flux composition may include one ormore components, such as a flowing agent, an oxidizing agent, a reducingagent or a purifying agent. Example flux compositions may includecarbonate of soda, potash, charcoal, coke, borax, lime, lead sulfide andphosphorus compounds. Still other flux compositions may includeinorganic chlorides, fluorides, limestone, litharge, activated carbonand other like materials. Still other flux compositions may includeionic salts, such as potassium nitrate, in a weight of up to 100% of theflux composition. In one aspect, the components of the flux compositionmay act as reducing agents to prevent oxide formation. In anotheraspect, components of the flux composition may act to selectivelypartition impurities away from the precious metal or other targetmaterial or add desirable elements to the target material.

A PTO may be combined with a flux composition in any suitable ratio. Forexample, a given amount of a PTO may be combined with a greater, smalleror equivalent amount of a flux composition in order to recover a targetmaterial from the PTO. In some embodiments, the combination may includeabout 25 to about 75 weight percent of the PTO or geologic material, andabout 25 to about 75 weight percent of the flux composition. Severalcombinations including a PTO and a flux composition are described in theExamples provided herein. However, maximum recovery of a target materialfrom some PTOs may require an adjustment of the percentage of individualcomponents of a flux composition as well as the total amount of the fluxcomposition combined with a PTO.

Another aspect of a system and method according to the presentdisclosure may include a milling step in order to grind or mix the PTOwith a flux composition. One objective of a milling step may be toprovide a generally homogeneous mixture of the combined PTO and fluxcomposition. A generally homogeneous mixture may be visibly uniform incolor or particle size. However, it may not be necessary that theproduct of a milling step is completely homogeneous. For example, a PTOand flux composition may be milled such that the flux composition has alarger, smaller or otherwise varied particle size and distribution incomparison with that of the PTO. Moreover, the portions of the fluxcomposition may be visually distinguished from the PTO after completionof a milling step, such as by a perceptible color, shape, or sizedifference.

In some embodiments, a milling step may be carried out with a ceramicmortar and pestle in order to prepare a sample combination including aPTO with a flux composition. The sample may be ground to the point whereit has a homogeneous or uniform color. In other embodiments, a suitablesized ball mill with ceramic balls may be used to mill a samplecombination. Other homogenization methods may also be used in a millingstep according to the present disclosure. Example methods may includeball milling, roller milling, hammer milling, and the like.

In one aspect, two or more milled samples may be combined. For example,a first milled combination of a PTO and a flux composition may becombined with a second milled combination of a PTO and a fluxcomposition. The first combination and second combination may havegenerally the same overall composition or the combinations may havedifferent compositions. In one example, fly ash may be combined with aborax-based flux composition in a first milling process, while minetailings may be combined with a litharge-based flux in a second millingprocess. Afterwards, the products of the first and second millingprocesses may be combined and optionally exposed to another milling ormixing step. In another example, a PTO material may be milled separatelyfrom a flux composition with the separately milled products combined ina later step. In still other examples, two or more sequential millingsteps may be carried out to achieve a suitable mixture of a PTO materialand a flux composition.

Another aspect of a method according to the present disclosure caninclude sintering a combination of a PTO material and a fluxcomposition. Generally, sintering may include heating a PTO material ata given temperature for a period of time in order to aid in the recoveryof a target material from the PTO. A sintering step may be carried out avarious points during a recovery or analysis process. In someembodiments, sintering may include heating of a PTO material alone or incombination with a flux composition. In other embodiments, sintering maybe carried out with a combination of a PTO material and flux compositionfollowing a milling step as described above. A milled combination may beplaced in a container made of a refractory material that is able towithstand the temperatures associated with a sintering step. Forexample, one possible container may include a fireclay saggar orsintering tray. A milled combination may be placed in a uniform layerwithin a sintering tray. A milled combination may also be dividedbetween two or more sintering trays. The prepared sintering trays may beplaced in a kiln, furnace, oven or other heating apparatus. Thesintering trays may remain static within the heating apparatus, or thetrays may be made to pass through a heating apparatus such asmulti-temperature zone belt furnace. Optionally, the sintering step maytake place above atmospheric pressure. In one aspect, a hot isostaticpressing process may be used.

A sintering step may include any suitable sintering temperature profile.In one aspect, a sample such as a milled combination of PTO and a fluxcomposition may be heated from room temperature to a set pointtemperature and held at the set point temperature for a period of time.A sample may be generally sintered at a set point temperature below themelting point of the sample. However, any set point temperature may beselected. In some embodiments, a sintering profile may include more thanone segment. For example, a first segment may include heating a sampleto a first set point temperature and holding the sample at thattemperature for a first period of time. In a second subsequent segment,a sample may be heated (or cooled) from the first set point temperatureto a second set point temperature and held at the second set pointtemperature for a second period of time. The first and second timeperiods may have the same duration or a different duration. Additionalsegments may also be included, such as a final cooling segment duringwhich a sample is returned to ambient conditions. In general, thesegments may be programmed with a temperature controller.

In some embodiments, a sintering step may be used to transition at leasta portion of the target material into a more readily detectable orrecoverable state. For example, a PTO including gold in a non-bulk statemay be sintered in the presence of a flux composition to cause the goldto transition from the non-bulk state into a bulk state. That is, asintering step may be configured to cause a portion of the targetmaterial to agglomerate into a bulk state. This transition may involvebreaking or forming of chemical or physical bonds. A sintering step mayalso increase the rate of atomic diffusion in order to encouragecoalescence of disparate gold atoms, particles or compounds, therebyyielding larger molecules that may be more readily detectable orrecoverable when transitioned into a bulk state.

For sintering steps with a temperature profile including two or moreheating segments, one or more of these segments may be configured topromote the initial formation of agglomerated gold clusters. Theagglomerated gold clusters may be derived from atomic gold particlesattached to amorphous colloidal silica contained within a PTO.Relaxation of bonding between the atomic gold particles and theamorphous colloidal silica may occur due to recrystallization,aurophilic attraction, or another mechanism. In one aspect, it may bepossible to recover atomic gold particles from amorphous colloidalsilica due to recrystallization of the amorphous colloidal silica tomicrocrystalline silicon dioxide. A weaker bond strength may existbetween atomic gold particles and microcrystalline silicon dioxide ascompared with amorphous colloidal silica allowing for the atomic goldparticles to be more readily recovered. In another aspect, aurophilicattraction between two or more atomic gold particles, at least one ofwhich is associated with amorphous colloidal silica, may result in theformation of larger agglomerated gold clusters. The formation of largergold clusters may lead to a weaker bond with the amorphous colloidalsilica allowing for the gold clusters to be more readily recovered.

In some embodiments, the resulting agglomerated gold clusters may bebelow bulk metal in size (i.e., in a non-bulk state) and therefore maynot be readily characterized or detected as metallic gold using standardanalytical methods. Segments of a temperature profile for initialformation of an agglomerated material may occur at relatively lowtemperatures. For example, if a sample will be ultimately sintered at amaximum temperature of about 900° C. (1650° F.), then a temperature ofabout 500° C. (930° F.) may be selected for a segment to enable theinitial agglomeration process to occur.

A temperature profile may also include a heating segment configured topromote the continued formation and growth of the agglomerated goldclusters into larger bulk metal clusters or critical size nuclei. Thelarger bulk metal clusters may then serve as loci for growth into largerparticles that may be recovered or characterized as gold metal. Segmentsof a temperature profile for the formation of larger bulk metal clustersmay occur at relatively moderate to high temperatures. For example, if asample will be ultimately sintered at a maximum temperature of about900° C. (1650° F.), then temperatures from about 700° C. (1290° F.) toabout 900° C. (1650° F.) may be selected for one or more heatingsegments to promote larger bulk metal cluster formation and ultimately,formation of recoverable or detectable, bulk state precious metals.

A sintering step may include a temperature profile with any number ofheating segments. In some embodiments, a temperature profile can includefour heating segments with each segment being characterized by holds atprogressively higher temperatures. For example, the set pointtemperatures for each sequential hold may be 500° C. (930° F.), 600° C.(1110° F.), 700° C. (1290° F.) and 900° C. (1650° F.) for heatingsegments 1-4, respectively. Other temperature profiles may include moreor less heating (or cooling) segments. Moreover, subsequent set pointtemperatures may be relatively higher or lower than a previous set pointtemperature. That is, the temperature may increase or decrease betweeneach heating segment in order to reach the new set point temperature.

The length of time for which a sample is maintained at the set pointtemperature once the set point temperature has been reached (i.e., thehold time) may also vary. In some embodiments, the hold time may bebetween about 5 minutes and about 5 hours. For example, a temperatureprofile may include segments where each segment includes a hold time ofabout 90 minutes. In another example, the hold time may vary with afirst heating segment having a hold time of about 60 minute, a secondheating segment having a hold time of about 120 minutes and subsequentheating segment having a hold time of 30 minutes. Longer or short holdtimes may be used and in some embodiments, or the hold time may beomitted altogether.

The rate at which the temperature is increased or decreased (i.e.,ramped) between set point temperatures may also vary. In someembodiments, it may be desirable to transition between set pointtemperatures at the maximum ramp rate achievable given thespecifications of the selected process equipment. In other embodiments,the ramp rate (degrees per unit time) may be controlled. For example, itmay be useful to use a temperature ramp rate (positive or negative) ofabout 1 to about 25° C. per minute. A controlled ramp rate may be usefulfor a temperature profiles that may not include one or more intermediateset point temperatures. Moreover, the ramp rate may vary as a functionof time or as the temperature profile for the sintering processprogresses.

For some PTO materials, a second stage sintering step may furtherpromote the transition of the target material (e.g., gold) from anon-bulk state to a bulk state that may be more readily recovered orcharacterized. Therefore, a system and method according to the presentdisclosure may include more than one distinct sintering step. Forexample, a sample such as a milled combination of PTO and a fluxcomposition may be subjected to a first stage sintering step followed bya second stage sintering step. The first stage sintering step maygenerally be carried out as described above with a sample being exposedto a complete temperature profile including a cooling step to return thesample to ambient conditions. The product of the first stage sinteringstep may then be subjected to one or more processing steps such as acombining or milling step as described herein. Following any processingsteps, the sample may be subjected to a second stage sintering processincluding exposure to a second complete temperature profile.

In one aspect, it may be useful for PTO materials run through a firstsintering profile to be re-ground to a given mesh size, combined andmilled with a second flux composition, and then re-sintered. Inparticular, the inventor has made the surprising discovery that for aPTO material including gold in a non-bulk state, the product of a milledcombination of the PTO and a flux composition might, after a first stagesintering step, be characterized by fire assay as having a gold contentof about 50 troy ounces per short ton (about 0.17 wt %). However, aftersecond stage sintering (following milling of the product of the firststage sintering step with an additional amount of a second fluxcomposition), a sample might be characterized by fire assay as having agold content of about 350 troy ounces per ton (about 1.2 wt %) or a7-fold increase in detectable gold.

The second flux composition may be the same or different from a firstflux composition if a first flux composition was added to the PTOmaterial prior to first stage sintering. The amount of a second stageflux composition combined with the product of a first stage sinteringstep may also vary with respect to an amount of a first flux composition(if any) combined with the PTO prior to the first stage sintering step.In one aspect, the product of a first stage sintering step may becombined with about 5% to about 50% of a second flux composition bytotal weight of the product of the first stage sintering step. Forexample, 20% by weight of a second flux composition may be added.Accordingly, for a product of a first stage sintering step weighing 10kg, 2 kg of a second flux composition may be combined with the product.As described above, this second combination may be subjected to milling,for example, to generally homogenize the combination prior to a secondstage sintering step.

As discussed previously, a second stage sintering step may be useful toincrease the amount of target material that may be recovered or detectedby several fold. One possible explanation for this detected increase maybe related to the effect of agglomerated particles or metal clustersacting as nucleation sites. In the example case of gold containing PTOmilled with a first flux composition, nucleation sites or “seeds” in theform of non-bulk state gold particles may be present after completion ofa first stage sintering step. However, it is possible that the rate ofnucleation or grain growth diminishes as portions of the fluxcomposition, which may promote mobility of the gold, react and combinewith the components of the PTO. One result may be that the sampleundergoing sintering is less viscous and the gold particles less mobile.The net effect may be to slow the rate of nucleation and possibly leavea portion of the gold particles in a non-bulk state that may not bereadily recovered or detected. Accordingly, recovery of additionaltarget material may be realized with a second stage sintering stepincluding an additional portion of a second flux composition.

Additional or alternative processing steps may also be included in asystem and method according to the present disclosure. For example, inaddition or as an alternative to a flux composition, a seed material maybe combined and milled with a PTO material. In one aspect about 0% toabout 10% of a seed material may be combined with a PTO material. Forexample, for the recovery of gold from a PTO sample, about 3% by weightof gold powder may be added to the PTO material. In one aspect, it maybe possible to determine whether or not the addition of an amount of aseed material may be able to promote the transition of a target materialfrom a non-bulk state to a bulk state. Accordingly, the addition of agiven amount of a seed material may be tested with each new PTO materialto determine if the addition of the seed material will have a positiveeffect on the rate of nucleation and growth of the particles or clustersof the target material. While the seed material may be incorporated atany point in the present system and method, in one aspect, the seedmaterial may be combined with the PTO for milling prior to first stagesintering. In another aspect, the seed material may be combined with theproduct of a first stage sintering step and milled prior to second stagesintering. Similarly, the seed material may be added before or after athird or subsequent sintering step or omitted altogether. Examples ofseed materials can include an ore containing the target material (e.g.,gold ore, platinum ore, etc.), pure bulk state particles of the targetmaterial (e.g., colloidal gold particles, gold powder), and materials ingeneral that may promote nucleation, particle growth, and transitionfrom the non-bulk state to the bulk state.

In some embodiments of the present system and method, the targetmaterial may be characterized, detected, recovered or otherwise assayed.A step of recovering or assaying may occur at any point in a processaccording to the present disclosure. In one example, a recovering orassaying step may occur following the completion of one or moresintering steps. Accordingly, a product of a first stage or second stagesintered material may be recovered and characterized to determine thecontent of the target material. The sintered product of a first stagesintering step may be characterized by fire assay as having a detectableamount of the target material, such as at least about 0.15 weightpercent gold in a bulk state. If the sintered product is then processedand exposed to a second stage sintering step, the resulting material maybe characterized by fire assay as having a higher amount of the targetmaterial than first detected, such as a gold content of at least about 1weight percent gold in a bulk state. Other analytical methods inaddition or as an alternative to a fire assay may be used to determinethe content of a target material. Moreover, samples may be analyzed atany point when carrying out a system and method according to the presentdisclosure. Intermittent analysis may be used, for example to obtain oneor more quantitative or qualitative measurements, such as mass, density,composition, and the like. Useful techniques may include spectroscopicanalysis, chemical assay, physical analysis, and other analyticalmethods.

In some embodiments, recovered sintered products may be processed torecover the target material using one or more recovery methods. Examplesof recovery methods may include liquid extraction with an aqua regia orsodium cyanide treatment, electrochemical extraction or any othersuitable technique for recovering target materials such as gold, silver,platinum group metals, and other precious metals in general. In otherembodiments, it may be economically viable to sell the targetmaterial-bearing sintered material without recovering or purifying thetarget material. For sintered products including other materials thatmay be useful to recover in addition to the target material, additionalor alternative processing steps may be performed to recover these othermaterials. For example, when a flux composition includes litharge (i.e.,lead oxide), due to the high lead content of the final sinter, it may beuseful to recover the lead in addition to the target material.

Referring to FIG. 1 an example method for recovering a target materialsuch as gold or another precious metal from a PTO may include a firststage and optionally a second stage. In general, a first stage forrecovering a target material of the method 100 may include a first step102 in which a PTO including a target material is prepared. Preparationof the target material may include any number of purification,separation, grinding, or other process steps. For example, the PTO maybe ground and passed through one or more sieves to obtain a fractionhaving a maximum particles size. In one aspect, a minimum U.S. standardmesh size of about 200-300 may be used to prepare the PTO material.

Once the PTO has been prepared, a next step 104 in a method 100 mayinclude combining the PTO (e.g., a geologic material including at leastone precious metal present in a non-bulk state) with a first stage fluxcomposition. One possible flux composition may include borax and calciumfluoride. However, other a flux composition may include other componentsas described herein. Optionally, a seed material such as a powdered orecontaining the target material may be combined with the PTO.

A next step 106 of the method 100 may include milling the combination ofstep 104 to provide a first stage mixture. Step 106 may include anysuitable milling apparatus, such as a ball mill or mortar and pestle.The first stage mixture may then be sintered in a step 108 of the method100. One aspect of step 108 may include transitioning a portion of thetarget material from a non-bulk state to a bulk state. Another aspect ofa sintering the first stage mixture may include a temperature profilewith one or more heating segments. The sintering temperature profile maycause a portion of the target material (e.g., precious metal) toagglomerate within the first stage mixture. In one example, the firststage mixture may be sintered for a first period of time at a firsttemperature and a second period of time at a second temperature. Thesecond temperature may be different (e.g., greater) than the firsttemperature. However, as discussed previously, the temperature profilemay include more or less heating segments with varied temperatures andtimes.

A method 100 may also include a further step 110 of recovering the firststage sintered material. In some embodiments, at least a portion of thetarget material present in the PTO may have transitioned to a bulk stateduring the sintering process in step 108. Accordingly, a first stagesintered material may include at least about 0.15 weight percent of thetarget material in the bulk state.

A method 100 may further include a step 112. One example of a step 112includes assaying a first, second, or subsequent stage sinteredmaterial. Assaying can include a fire assay or another chemical orphysical characterization technique. In one aspect, the assay may beused to determine the target material content of the geologic material.While step 112 is illustrated as following step 110, a step of assayingmay take place at any point in the method 100 where it might be usefulto determine the composition or another property of a PTO sampleundergoing processing.

In some embodiments, the weight percent detected may be improved if thefirst stage sintered material is subjected to subsequent stages as shownfor the method 200 in FIG. 2. Accordingly, a method 200 may include tostep 202 in which a first stage sintered material (e.g., prepared bymethod 100) is prepared for second stage sintering. For example, thefirst stage sintered material may be prepared in a manner analogous tothe preparation of the PTO material as described for step 102 of method100. Method 200 may continue through the second stage including a step204 in which the first stage sintered material may be combined with asecond stage flux composition and optionally a seed material. Thecombination of step 204 may be milled to provide a second stage mixturein step 206, sintered in a step 208, and recovered in a step 210. As forstep 112 of method 100, method 200 may include a step 212 in which thesecond stage sintered material is assayed to measure the content orpurify the target material.

In some embodiments, a second stage as illustrated in method 200 maydiffer from a first stage as illustrated in method 100. For example, thefirst and second flux compositions may differ. The amount of flux addedto the first stage sintered material in the second stage may also differfrom the amount of flux added to the PTO material in the first stage.Other differences between the first and second stages may include thesintering profile, the milling apparatus, and the use of a seedmaterial. A third, fourth or subsequent stage may also be carried inaddition to (or instead of) method 100 and method 200.

In some embodiments, it may be useful to combine a PTO material withurea (CO(NH₂)₂), a surfactant, or a combination thereof for the recoveryof a target material. In one aspect, the urea and surfactant (eitheralone or in combination) may facilitate washing or purification of thePTO material. In another aspect, the urea and surfactant (either aloneor in combination) may assist in the nucleation, growth and recovery ofa target material from the PTO. For example, urea, a surfactant, or acombination thereof may be used to control the pH of a slurry includingthe PTO, facilitate the dispersion of particles of the PTO in theslurry, or otherwise facilitate the recovery of the target material fromthe PTO. In one example, urea may be added to a slurry of PTO to a finalconcentration of about 1 g/L to about 100 g/L. In another example, asurfactant may be added to a slurry of PTO to a final concentration ofabout 0.01% to about 1% on a volume per volume basis in the case of aliquid surfactant.

Suitable surfactants for use in the recovery of a target material fromPTO may include anionic, cationic, amphoteric (zwitterionic) andnon-ionic surfactants. Examples of anionic surfactants includealkylbenzene sulfonates, fatty acid soaps, lauryl sulfate, dialkylsulfosuccinate, lignosulfonates, and the like. Example of cationicsurfactants include quaternary alkylammonium compounds, fatty aminesalts, linear diamines, aromatic or saturated heterocycles including oneor more nitrogen atoms, and the like. Examples of nonionic surfactantsinclude ethoxylated linear alcohols, ethoxylated alkyl phenols, fattyacid esters, amine and amide derivatives, alkylpolyglucosides,ethleneoxide/propyleneoxide copolymers, polyalcohols and ethoxylatedpolyalcohols, thiols, and the like. Examples of amphoteric surfactantsinclude amino propionic acids, imido propionic acids, quaternizedcompounds such as betaines, sulfobetaines and taurines, and the like. Insome embodiments, it may be useful to provide a polyethylene oxide basednon-ionic surfactant such as polyethylene glycolp-(1,1,3,3-tetramethylbutyl)-phenyl ether (i.e., Triton X-100, DOWCHEMICAL CO.).

In one example method including the use of urea and a surfactant, atarget material may be recovered from a PTO by first forming a slurry ofthe PTO in an amount of water (e.g., tap water). In one aspect, the PTOmaterial may be prepared with a U.S. standard mesh size of about 300mesh, ensuring a PTO particle size of 300 mesh (equivalent to about 50μm) or smaller. In another aspect, the water may be combined with thePTO at a ratio of about 50 g PTO per liter of water. The slurry may beagitated in any suitable agitation apparatus. Further, it may be usefulto maintain a basic pH during agitation. For example, it may be usefulto maintain the pH between about 10.5 and about 11.5. The pH may bemaintained in any suitable fashion, such as through the addition of aconcentrated solution of NaOH. For recovery of the solid fraction of theslurry from the agitation apparatus, the slurry may be allowed to settlefor a period of time. Recovery may be further assisted by vacuumfiltration or another means of mechanical separation (e.g., filterpress). In one aspect, it may not be necessary to completely dry therecovered filter cake (solid fraction) prior to further processing. Forexample, it may be useful to proceed to a next step in a method forrecovering a target material from the PTO even though the filter cakecontains water.

Following an initial washing step as described above, it may be usefulto add an amount of urea, a surfactant, or a combination thereof to thewashed PTO. For example, a filter cake may be resuspended in a volume ofwater with an amount of urea. In one aspect, the volume of water may beequal to the first amount of water added to the PTO in the washing step(i.e., about 1 liter of water per 50 g PTO). In another aspect, the ureamay be added to the slurry to provide a final concentration of about 1g/L to about 100 g/L. In one particular example, the urea may be addedto the slurry to provide a final concentration of about 10 g/L. The ureamay be added to the slurry with continuous or intermittent agitation.Alternatively, agitation may be paused during addition of the urea or aportion thereof. The slurry with urea may be agitated for a period oftime (e.g., about 1 hour). Further, it may be useful to monitor the pHduring agitation. For example, the pH of the slurry may be between about9 and about 10.

Before or after the addition of urea, it may be useful to add an amountof a surfactant to the slurry. A surfactant may be added to a slurry ofPTO to a final concentration of about 0.01% to about 1% on a volume pervolume basis. In one example, the surfactant may be added to the slurryto provide a final concentration of about 0.01%. In another example, thesurfactant may be the non-ionic surfactant Triton-X 100. Alternatively(or in addition), the surfactant may be another suitable surfactant orcombination of surfactants such as one or more of the surfactantsdescribed above. The surfactant may be added to the slurry withcontinuous or intermittent agitation. Alternatively, agitation may bepaused during addition of the surfactant or a portion thereof. Theslurry with surfactant may be agitated for a suitable period of time(e.g., about 4 hour).

Following agitation in the presence of urea, a surfactant or acombination thereof, the solid fraction may be recovered from the slurryas a filter cake. Further steps may be carried out with the filter cakeincluding a sintering step, a mechanical shearing (attrition) step, oran assaying step to determine the amount of the target material presentin the PTO. Further, it may be useful to concentrate an attritedmaterial through gravity concentration. In one aspect, it has beendetermined that at least a portion of an attrited sample may beconcentrated by carefully washing the fines from the coarser metallicparticles. In another aspect, it may be useful to concentrate theattrited material with a slimes gravity table, a mineral jig, or thelike. By panning, concentrate ratios of approximate 20:1 have beenachieved. Further aspects of a method including the treatment of a PTOmaterial with urea, a surfactant, or a combination thereof are describedin Examples 8 and 9 below.

Turning now to FIG. 3, an example method 300 for recovering a targetmaterial from a PTO includes a first step 302 of preparing a PTOmaterial. The PTO may be prepared in any suitable fashion as describedherein. For example, the PTO material may be ground and sieved toprovide a material having a uniform particle size or distribution ofparticles sizes. A step 304 of the method 300 may include combining theprepared PTO material with water to provide a first slurry. In a nextstep 306, the first slurry may be agitated to wash the PTO material. Astep 308 may then include recovering a first solid fraction of materialfrom the first slurry.

In a next step 310 of the method 300, the first solid fraction may becombined with water, urea and a surfactant to provide a second slurry.The amount of urea, water and the surfactant may vary as describedherein. In one aspect, either the urea or the surfactant may be omittedor substituted for another component. Further, the urea and thesurfactant may be added simultaneously or sequentially to the solidfraction and the water in the second slurry. A further step 312 mayinclude agitating the second slurry. Agitation may occur before, during,and after addition of the urea and the surfactant to the second slurry.In a next step 314 of the method 300, a second solid fraction may berecovered from the second slurry. Recovery of either the first solidfraction in the step 308 or the second solid fraction in the step 314may include gravity filtration, vacuum filtration, a filter press, oranother suitable method of filtration.

A step 318 of the method 300 may include sintering the second solidfraction. Sintering may include firing of the second solid fraction in afireclay saggar. The saggar may be placed in an oven, kiln or the like.Further, a temperature program may be used in the step 318. The step 318may further include a mechanical shearing or attrition step. In thiscase, the attrited material may be concentrated to provide an attritedsinter for analysis. In a next step 320, the sintered material may beassayed to determine a percent of the target material present in thesintered material. In one aspect, the step 320 may include performing afire assay. In the case of a fire assay, the sintered material may becombined with a flux composition such as the composition described inTable 8 below.

The schematic flow charts shown in the Figures are generally set forthas a logical flow chart diagram. As such, the depicted order and labeledsteps are indicative of one embodiment of the presented method. Othersteps and methods may be conceived that are equivalent in function,logic, or effect to one or more steps, or portions thereof, of theillustrated method. Additionally, the format and symbols employed in theFigures are provided to explain the logical steps of the method and areunderstood not to limit the scope of the method. Although various arrowtypes and line types may be employed, they are understood not to limitthe scope of the corresponding method. Indeed, some arrows or otherconnectors may be used to indicate only the logical flow of the method.For instance, an arrow may indicate a waiting or monitoring period ofunspecified duration between enumerated steps of the depicted method.Additionally, the order in which a particular method occurs may or maynot strictly adhere to the order of the corresponding steps shown.

Example 1

A PTO material containing gold in a non-bulk state was processed inorder to recover gold from the PTO material. A 1 kg sample of a PTOmaterial (bottom ash) was combined with a flux composition (Table 1) anddivided into five approximate portions.

TABLE 1 Component Chemical Formula Parts Details Bottom Ash n.a. 100200-300 mesh size (US) Borax Powder Na₂B₄O₇•5H₂O 60 20-40 mesh CalciumFluoride CaF₂ 7 Gold Ore n.a. 5 powdered, optional n.a. = not applicable

Prior to combining with the flux composition, the PTO was processed toachieve a minimum U.S. standard mesh size of 200 to 300. The fluxcomposition included borax powder and calcium fluoride. In one aspect,the borax may reduce the melting point of minerals present in the PTO,including gold (T_(m)=1063° C.). In another aspect, calcium fluoride mayfunction as an activator to promote the dissolution of metal oxides,among other features.

Each of the five portions was milled with a ceramic mortar and pestleuntil the color of the combination was generally homogeneous. The fiveportions were then blended in a plastic bucket using a large plasticspoon and the blend was passed through a small impact mill twice. Themass of all of the PTO material and the flux composition was recordedbefore and after each of the combining and mixing steps. The combinedmaterial was then divided and processed into uniform layers in a numberof fireclay saggars (sintering trays). The milled combination was thensintered according to the profile shown in Table 2. Optional heatingsegment 4 was omitted.

TABLE 2 Segment Ramp Rate (° C./hr) Hold Temp. (° C.) Hold Time (min) 0n.a. R.T. n/a 1 maximum 500 90 2 maximum 607 90 3 maximum 727 90 4*maximum 899 90 5 n.a. R.T. n/a *optional heating segment; R.T. = room(ambient) temperature; n.a. = not applicable

Sintering was carried out in a programmable Super Dragon Kilnmanufactured by Paragon Industries, L.P. This kiln had a maximumoperating temperature of 1260° C. (2300° F.) with an average maximumramp rate of about 22° C. (72° F.) per minute. In general, the totalramping time from ambient temperature to 732° C. (1350° F.) for the kilnwas approximately 1 hour and the total sintering time for four 90 minuteheating segments as in Table 2 was approximately 5 hours and 30 minutesuntil furnace shut-off.

Heating segments 1 and 2 in Table 2 were configured for the lowtemperature initial formation of agglomerated gold clusters, whileheating segment 3 was configured for the continued formation and growthof these small clusters into larger bulk metal clusters as describedabove.

For second stage sintering the product of first stage sintering wascombined and milled with an additional 20% by weight of a second fluxcomposition composed of only borax powder. The second stage sinteringprofile was analogous to the first stage sintering profile as describedabove and shown in Table 2.

Example 2

The flux composition shown in Table 3 was substituted for the fluxcomposition shown in Table 1 and the process of Example 1 was applied. APTO combined with a flux composition including litharge may also besintered using a temperature profile as in Table 2 including optionalheating segment 4.

TABLE 3 Component Chemical Formula Parts Details Geologic Material n.a.100 200-300 mesh size (US) Litharge PbO 150 Calcium Fluoride CaF₂ 7 GoldOre n.a. 8 Powdered, optional n.a. = not applicable

Example 3

The flux composition shown in Table 4 was substituted for the fluxcomposition shown in Table 1 and the process of Example 1 was applied.

TABLE 4 Component Chemical Formula Parts Details Geologic Material n.a.100 200-300 mesh size (US) Activated Carbon n.a. 60 20-40 mesh size (US)Calcium Fluoride CaF₂ 7 Gold Ore n.a. 5 powdered, optional n.a. = notapplicable

A U.S. standard mesh size of 20 corresponds to a maximum particle sizeof about 0.853 mm and a mesh size of 40 corresponds to a maximumparticles size of about 0.422 mm.

Example 4

A method for recovering and refining gold from sintered material mayinclude a liquid extraction with aqua regia. For sinters that may notcontain litharge or significant amounts of lead, a 4:1 HCl:HNO₃composition of aqua regia may be used to recover in excess of 95% of thegold content as determined by fire assay. Recovery may be performed byheating just below the boiling temperature in a covered vessel forgreater than two hours with occasional stirring. Following heating, theaqua regia leach may be cooled to room temperature and vacuum filtered.The recovered filter residue may be washed with a volume of waterapproximately equal to the volume of the filtrate. The filter residuemay then be dried and fire assayed. The filter residue may be treatedwith a second portion of aqua regia as above to recover any remaininggold. The washed filter residue may be discarded.

Urea may be added to the filtrate with stirring until bubbling, whichindicates decomposition of HNO₃, is no longer observed. The filtrate maybe passed through a filter a once more to remove any remaining residue.The resulting filtrate may be golden yellow in color. A colloidal goldsuspension may be recovered through the addition of a hot, aqueoussolution of concentrated sodium metabisulfite. The solution may be addedwith stirring to the filtrate to achieve a final concentration of atleast 50 grams sodium metabisulfite per liter of filtrate. Thesuspension may settle for several hours to overnight and the goldrecovered by vacuum filtration. The filtrate may be washed with waterand dried. The resulting brown powder may have a gold content of up to95% or more.

Example 5

A method for recovering and refining gold from sintered material mayinclude a liquid extraction with sodium cyanide using standard methodsknown in the art. The use of sodium cyanide may result in a high yieldrecovery of gold in combination with the flux compositions described inTables 1 and 4.

Example 6

A method for recovering and refining gold from sintered materialincluding at least a potion of litharge or lead may be carried out asfollows. In order to reduce the litharge to lead so that it may beformed into a gold-bearing lead anode bar it may first be smelted atabout 1090° C. (2000° F.). The smelting process may include a fluxcomposition as shown in Table 5.

TABLE 5 Component Chemical Formula Parts Details Sinter Including n.a.100 Target Material Activated Carbon n.a. 30 20-40 mesh size (US) SodiumCarbonate Na₂CO₃ 20 Borax Powder Na₂B₄O₇•5H₂O 180 n.a. = not applicable

Using a silicon carbide crucible, the flux composition may be backcharged into the crucible. In one aspect, this may reduce thepossibility of the charge overflowing the crucible. The charge may thenbe smelted for about 1.5 to 2 hours at a temperature of about 1090° C.(2000° F.). The resulting smelt may be poured into a flat bottom castiron mold to provide a suitable lead/gold plate that may be anodeleached. The casting may be cooled and any slag may be removed from thelead bar, for example, with a small hammer.

One or more electrochemical tanks may be prepared to receive the castbars. One possible electrolyte composition includes a 25% aqueoussolution of lead fluoroborate. A DC rectifier may be configured tosupply adequate amperage. During operation, the electrolyte may beslowly recirculated, such as with a peristaltic pump and acid resistantplastic tubing. The gold-bearing lead bar may be configured as the anodeand a stainless steel plate as the cathode. In order to contain the goldslimes, an anode bag may be used with each lead bar in theelectrochemical tank. The lead from the cathode may be scrapped offperiodically and any lead in the bottom of the tank may be periodicallyremoved by coarse filtration. The voltage in the tank may be maintainedat about 3.5 volts DC. The resulting gold-bearing mud may be washed fromthe anode bag, dried, and smelted to a gold ore. Additional anode barsmay be added to the electrochemical tanks and the anode leaching processcontinued. Remaining lead “heels” from the anode leaching may be addedto the above smelting process and thus recycled.

Example 7

A system and method for recovering and refining gold from a sinteredmaterial may include determining the gold content by fire assay. In oneaspect, each of the major steps in a system and method according to thepresent disclosure may be fire assayed for gold content.

One possible flux composition for use in a fire assay to determineeither gold or silver content is shown in Table 6.

TABLE 6 Component Chemical Formula Mass (g) Sample Including TargetMaterial n.a. 5 Litharge PbO 40 Flour n.a. 2.5 Sodium Carbonate Na₂CO₃30 Borax Powder Na₂B₄O₇•5H₂O 15 Silica SiO₂ 3 n.a. = not applicable

The composition illustrated in Table 6 may be smelted using a 30 gramfire clay crucible at a temperature of 1038° C. (1900° F.) for a periodof 1 hour. The melt may be poured into a cast iron mold and aftercooling, the slag may be cleaned from the resulting lead button using,for example, a small hammer. The resulting lead button may be cupelledusing a magnesite composition cupel at a temperature of 1010° C. (1850°F.). The resulting ‘gold’ prill may be weighed with a milligram scaleand the prill evaluated for possible silver content. The gold contentmay be determined, for example, in units of Troy ounces per ton (TO/T)of the sample.

Example 8

Another example method for the recovery of a target material from a PTOmaterial containing gold in a non-bulk state may include the use of ureaand a surfactant. For washing of the PTO, a quantity of PTO material wasprocessed to achieve a minimum U.S. standard mesh size of at least about300 (i.e., a particle size of less than about 50 μm). The processed PTOwas combined with tap water at a ratio of 1 liter of tap water per 50grams of PTO material. The water and PTO were placed in an agitationsystem including a plastic tank with baffle plates. During agitation ofthe PTO material, a sufficient amount of NaOH, in the form of causticsoda micropearls, was added to the system as necessary to maintain a pHof between about 10.5 and about 11.5.

Following 1 hour of agitation, the solid fraction was allowed to settlefor at least about 15 minutes. The settled slurry was filtered torecover the solid fraction, and the filtrate (liquid fraction) wasdiscarded. To achieve nucleation and growth of the gold material withinin the PTO, the remaining moist filter cake including the solid fractionwas returned to the agitation system with a volume of tap water equal tothe initial volume added to the PTO in the previous agitation step(i.e., 1 liter water per 50 g PTO). Under moderate agitation, urea wasadded to the system at a ratio of 10 grams of urea per liter of slurry.Following the addition of urea, agitation was continued for 1 hour andthe pH was monitored. The pH of the slurry during nucleation and growthwas between about 8 and about 9. Thereafter, a non-ionic surfactant wasadded to the still agitating slurry at a ratio of 1 ml Triton X-100 (DOWCHEMICAL) per liter slurry. Agitation was then continued for 4 hoursfollowed by filtration of the solid fraction from the slurry. Theresulting filter cake including the solid fraction was exposed to a“Blow-down” process, in which concentrated air is blown onto the filtercake to remove excess water until the filter cake is nearly dry.

For sintering, the moist solid fraction was added to fire clay saggarswith a layer thickness of no more than about 25 mm to about 50 mm. Thesaggars were placed in a furnace programmed according to the methodshown in Table 7.

TABLE 7 Segment Ramp Rate (° C./hr) Hold Temp. (° C.) Hold Time (min) 0n.a. R.T. n/a 1 maximum 260 60 2 maximum 680 60 3 maximum 1090 60 4 n.a.R.T. n/a R.T. = room (ambient) temperature; n.a. = not applicable

Following completion of the program in Table 7, the saggars were removedfrom the furnace and allowed to cool. The sinter was recovered from thecooled saggars, coarse-ground, and weighed.

For metallization of the nucleated fraction of the precious metal, thecoarse-ground sintered material was mechanically attrited (i.e., exposedto a shearing force) for between about 4 to about 8 hours as determinedby assaying the attrited material on an hourly basis. When the amount ofprecious metal recovered from the attrited material reached asteady-state value, verified microscopically during the assay processthat was repeated hourly, the attrition process was determined to becomplete. Following attrition, the resulting material was tested for theability to gravity concentrate. The attrited material was concentratedby washing the fines from the coarser metallic particles. The resultingattrited sinter was assayed using conventional methods as describedherein.

Example 9

Another possible flux composition for use in performing a fire assay todetermine either gold or silver content is shown in Table 8. In oneaspect, the flux composition in Table 8 may be useful for the analysisof samples prepared with urea, a surfactant, or a combination thereof.

TABLE 8 Component Chemical Formula Mass (g) Sample Including TargetMaterial n.a. 2 Litharge PbO 40 Flour n.a. 8 Sodium Carbonate Na₂CO₃ 40Borax Powder Na₂B₄O₇•5H₂O 15 Calcium Fluoride CaF₂ 2 Silica SiO₂ 3Analytical Grade Silver Powder Ag 0.5 n.a. = not applicable

The composition illustrated in Table 8 may be prepared a 30 gram fireclay crucible and placed in a furnace or kiln at a temperature of 500°C. (986° F.) for a period of 1 hour followed by a temperature ramp to1093° C. (2000° F.). When the temperature of the furnace reaches 1093°C. (2000° F.), the melt may be poured from the crucible into a cast ironmold. After cooling, the slag may be cleaned from the resulting leadbutton using, for example, a small hammer. The resulting lead button maybe cupelled using a magnesite composition cupel at a temperature of1010° C. (1850° F.). The resulting ‘gold’ prill may be weighed with amilligram scale and the prill evaluated for possible silver content. Thegold content may be determined, for example, in units of Troy ounces perton (TO/T) of the sample.

In another aspect, following cupellation at 1010° C. (1850° F.), theresulting product may undergo a parting process to separate any goldpresent in the sample from any silver present in the sample. An acidparting process may involve the addition of the sample to a solution of30% HNO₃ prepared with distilled water. The parting step may be carriedout at low temperature (e.g., less than about 95° C.). Materialresulting from the parting process (i.e., partings) may be washed withdistilled water and annealed at a temperature of about 600-675° C. Theannealed material may then be weighed or otherwise analyzed to determinethe gold content. A further step may include regrinding the slag to afine powder. The ground slag may be refired or panned.

In the above example, it may be useful to include the initial step ofholding the crucible at a temperature of 500° C. (986° F.) for a periodof 1 hour to facilitate the reduction of the litharge (PbO) to lead (Pb)in the presence of flour (reductant) while the melt is still relativelyviscous. In doing so, the small globules of Pb/PbO may have a betterchance of reacting with the very small particles of nucleated gold.Further discussion of this phenomenon may be found here: Lashley, W.(1985). Fundamentals of Fire Assaying (an introduction to Slagmaster).p. 4, Bul. 113084A, American Society for Applied Technology.

The present invention has been described in terms of one or morepreferred embodiments, and it should be appreciated that manyequivalents, alternatives, variations, and modifications, aside fromthose expressly stated, are possible and within the scope of theinvention.

Each reference identified in the present application is hereinincorporated by reference in its entirety.

While present inventive concepts have been described with reference toparticular embodiments, those of ordinary skill in the art willappreciate that various substitutions and/or other alterations may bemade to the embodiments without departing from the spirit of presentinventive concepts. Accordingly, the foregoing description is meant tobe exemplary, and does not limit the scope of present inventiveconcepts.

A number of examples have been described herein. Nevertheless, it shouldbe understood that various modifications may be made. For example,suitable results may be achieved if the described techniques areperformed in a different order and/or if components in a describedsystem, architecture, device, or circuit are combined in a differentmanner and/or replaced or supplemented by other components or theirequivalents. Accordingly, other implementations are within the scope ofthe present inventive concepts.

What is claimed is:
 1. A method for recovering a precious metal from ageologic material, the method comprising the steps of: (a) forming aslurry including: (i) a geologic material including at least oneprecious metal, the at least one precious metal being present in anon-bulk state, and (ii) a surfactant; (b) agitating the slurry; (c)recovering a solid fraction from the agitated slurry; and (d) sinteringthe solid fraction according to a first sintering profile that causes aportion of the at least one precious metal to agglomerate within thesolid fraction into a bulk state of the at least one precious metal, theat least one precious metal having in the bulk state a greater weightpercent of the solid fraction than the at least one precious metal hadprior to sintering the solid fraction.
 2. The method of claim 1, whereinthe step (a) further comprises forming a slurry including urea.
 3. Themethod of claim 1, wherein the at least one precious metal is selectedfrom gold, silver and platinum group metals.
 4. The method of claim 1,wherein a portion of the at least one precious metal is present asatomic clusters bonded to amorphous colloidal silica.
 5. The method ofclaim 4, wherein the composition of the slurry and the first sinteringprofile are selected to separate the atomic clusters from the amorphouscolloidal silica.
 6. The method of claim 1, wherein the geologicmaterial is selected from mine tailings and coal combustion products. 7.The method of claim 2, wherein the urea is added to the slurry toprovide a final concentration of about 1 gram per liter to 100 grams perliter.
 8. The method of claim 1, wherein the surfactant is added to theslurry to a final concentration of about 0.01% to about 1% on a volumeper volume basis.
 9. The method of claim 1, wherein the slurry comprisesabout 50 g of the geologic material per 1 liter of water.
 10. The methodof claim 1, wherein the first sintering profile includes a first periodof time at a first temperature and a second period of time at a secondtemperature, wherein the second temperature is greater than the firsttemperature.
 11. The method of claim 10, wherein the first temperatureis at least about 260 degrees Celsius, and wherein the secondtemperature is at least about 680 degrees Celsius.
 12. The method ofclaim 1, further comprising washing the geologic material prior toforming the slurry.
 13. The method of claim 1, wherein the surfactant ispolyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether.
 14. Amethod for recovering gold from a geologic material, the methodcomprising the steps of: (a) combining into a first slurry: (i) ageologic material including gold present in a non-bulk state, and (ii)about 1 liter of water per 50 grams of the geologic material; (b)agitating the first slurry; (c) recovering a first solid fraction fromthe first slurry; (d) combining into a second slurry: (i) the firstsolid fraction, (ii) about 1 liter of water per 50 g of the geologicmaterial, (iii) about 1 gram per liter to about 100 grams per liter ofurea, and (iv) about 0.01% to about 1% of a non-ionic surfactant on avolume per volume basis; (e) agitating the second slurry; (f) recoveringa second solid fraction from the second slurry; (g) sintering the secondsolid fraction for a first period of time at a first temperature, asecond period of time at a second temperature, and a third period oftime at a third temperature, wherein the second temperature is greaterthan the first temperature, and the third temperature is greater thanthe second temperature; and (h) recovering a sintered material includingat least about 0.15 weight percent of gold metal in a bulk state. 15.The method of claim 14, wherein the geologic material is selected frommine tailings and coal combustion products.
 16. The method of claim 14,wherein the second slurry comprises about 10 grams per liter of urea.17. The method of claim 14, wherein the second slurry comprises about0.1% of the surfactant on a volume per volume basis.
 18. The method ofclaim 14, wherein the first temperature is at least about 260 degreesCelsius, wherein the second temperature is at least about 680 degreesCelsius, and wherein the third temperature is at least about 1090degrees Celsius.
 19. The method of claim 14, wherein the surfactant ispolyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether.
 20. Themethod of claim 14, further comprising a step of mechanically attritingthe sintered material.